Library /sys$common/syshlp/nclhelp.hlb set, routing, circuit, manual L2only mode  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Support: L2
    Default: False         Value: True or false

    If true, specifies that this circuit is to be used only for level
    2 traffic. If false, the circuit may be used for both level 1 and
    level 2 traffic. You can modify this characteristic only when the
    entity is disabled.